Each day a different image or photograph is featured, with an
accompanying caption, which deals with various topics in Earth Science.

Mendenhall Glacier

The photo above showing the magnificent Mendenhall Glacier was captured from Juneau, Alaska, in the southeastern part of the state, on August 21, 2009. Mendenhall Glacier’s maximum advance occurred near 1700, when its terminus was positioned nearly 2.5 miles (4 km) down valley from its current location. In the mid 1700s, it began to retreat as its annual rate of melt exceeded its annual total accumulation – negative mass balance. The Juneau Icefield is the source area of the Mendenhall Glacier.

The blue coloration of the ice is not at all related to reflection from the sky but rather to absorption as a result of multiple scattering of light by myriad ice particles. Both water and ice absorb slightly more in the red (long wavelength) than in the blue (short wavelength) part of the electromagnetic spectrum. After sunlight has been scattered and absorbed thousands of times by ice (or snow) crystals, the reds, oranges and yellows can no longer be detected -- only blue and green light remains. As shown here, the ablation zone is often stained with dust and debris during the summer season.